text: ///////////////////////////////////////////////////////////////////////////////
  // throttle will transform a topic to have a limited number of bytes per second
  //
  // Copyright (C) 2009, Morgan Quigley
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //   * Redistributions of source code must retain the above copyright notice,
  //     this list of conditions and the following disclaimer.
  //   * Redistributions in binary form must reproduce the above copyright
  //     notice, this list of conditions and the following disclaimer in the
  //     documentation and/or other materials provided with the distribution.
  //   * Neither the name of Stanford University nor the names of its
  //     contributors may be used to endorse or promote products derived from
  //     this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  /////////////////////////////////////////////////////////////////////////////
  
  
  // this could be made a lot smarter by trying to analyze and predict the
  // message stream density, etc., rather than just being greedy and stuffing
  // the output as fast as it can. 
  
  #include <cstdio>
  #include <cstdlib>
  #include <deque>
  #include "topic_tools/shape_shifter.h"
  #include "topic_tools/parse.h"
  
  using std::string;
  using std::vector;
  using std::deque;
  using namespace topic_tools;
  
  // TODO: move all these globals into a reasonable local scope
  ros::NodeHandle *g_node = NULL;
  uint32_t g_bps = 0; // bytes per second, not bits!
  ros::Duration g_period; // minimum inter-message period
  double g_window = 1.0; // 1 second window for starters
  bool g_advertised = false;
  string g_output_topic;
  string g_input_topic;
  ros::Publisher g_pub;
  ros::Subscriber* g_sub;
  bool g_use_messages;
  ros::Time g_last_time;
  bool g_use_wallclock;
  bool g_lazy;
  ros::TransportHints g_th;
  
  class Sent
  {
  public:
    double t;
    uint32_t len;
    Sent(double _t, uint32_t _len) : t(_t), len(_len) { }
  };
  deque<Sent> g_sent;
  
  void conn_cb(const ros::SingleSubscriberPublisher&);
  void in_cb(const ros::MessageEvent<ShapeShifter>& msg_event);
  
  void subscribe()
  {
    g_sub = new ros::Subscriber(g_node->subscribe(g_input_topic, 10, &in_cb, g_th));
  }
  
  void conn_cb(const ros::SingleSubscriberPublisher&)
  {
    // If we're in lazy subscribe mode, and the first subscriber just
    // connected, then subscribe, #3546
    if(g_lazy && !g_sub)
    {
      ROS_DEBUG("lazy mode; resubscribing");
      subscribe();
    }
  }
  
  void in_cb(const ros::MessageEvent<ShapeShifter>& msg_event)
  {
    boost::shared_ptr<ShapeShifter const> const &msg = msg_event.getConstMessage();
    boost::shared_ptr<const ros::M_string> const& connection_header = msg_event.getConnectionHeaderPtr();
  
    if (!g_advertised)
    {
      // If the input topic is latched, make the output topic latched
      bool latch = false;
      if (connection_header)
      {
        ros::M_string::const_iterator it = connection_header->find("latching");
        if((it != connection_header->end()) && (it->second == "1"))
        {
          ROS_DEBUG("input topic is latched; latching output topic to match");
          latch = true;
        }
      }
      g_pub = msg->advertise(*g_node, g_output_topic, 10, latch, conn_cb);
      g_advertised = true;
      printf("advertised as %s\n", g_output_topic.c_str());
    }
    // If we're in lazy subscribe mode, and nobody's listening, 
    // then unsubscribe, #3546.
    if(g_lazy && !g_pub.getNumSubscribers())
    {
      ROS_DEBUG("lazy mode; unsubscribing");
      delete g_sub;
      g_sub = NULL;
    }
    else
    {
      if(g_use_messages)
      {
        ros::Time now;
        if(g_use_wallclock)
          now.fromSec(ros::WallTime::now().toSec());
        else
          now = ros::Time::now();
        if (g_last_time > now)
        {
          ROS_WARN("Detected jump back in time, resetting throttle period to now for.");
          g_last_time = now;
        }
        if((now - g_last_time) > g_period)
        {
          g_pub.publish(msg);
          g_last_time = now;
        }
      }
      else
      {
        // pop the front of the queue until it's within the window
        ros::Time now;
        if(g_use_wallclock)
          now.fromSec(ros::WallTime::now().toSec());
        else
          now = ros::Time::now();
        const double t = now.toSec();
        while (!g_sent.empty() && g_sent.front().t < t - g_window)
          g_sent.pop_front();
        // sum up how many bytes are in the window
        uint32_t bytes = 0;
        for (deque<Sent>::iterator i = g_sent.begin(); i != g_sent.end(); ++i)
          bytes += i->len;
        if (bytes < g_bps)
        {
          g_pub.publish(msg);
          g_sent.push_back(Sent(t, msg->size()));
        }
      }
    }
  }
  
  #define USAGE "\nusage: \n"\
             "  throttle messages IN_TOPIC MSGS_PER_SEC [OUT_TOPIC]]\n"\
             "OR\n"\
             "  throttle bytes IN_TOPIC BYTES_PER_SEC WINDOW [OUT_TOPIC]]\n\n"\
             "  This program will drop messages from IN_TOPIC so that either: the \n"\
             "  average bytes per second on OUT_TOPIC, averaged over WINDOW \n"\
             "  seconds, remains below BYTES_PER_SEC, or: the minimum inter-message\n"\
             "  period is 1/MSGS_PER_SEC. The messages are output \n"\
             "  to OUT_TOPIC, or (if not supplied), to IN_TOPIC_throttle.\n\n"
  
  int main(int argc, char **argv)
  {
    if(argc < 3)
    {
      puts(USAGE);
      return 1;
    }
  
    g_input_topic = string(argv[2]);
  
    std::string topic_name;
    if(!getBaseName(string(argv[2]), topic_name))
      return 1;
  
    ros::init(argc, argv, topic_name + string("_throttle"),
              ros::init_options::AnonymousName);
    bool unreliable = false;
    ros::NodeHandle pnh("~");
    pnh.getParam("wall_clock", g_use_wallclock);
    pnh.getParam("unreliable", unreliable);
    pnh.getParam("lazy", g_lazy);
  
    if (unreliable)
      g_th.unreliable().reliable(); // Prefers unreliable, but will accept reliable.
  
    if(!strcmp(argv[1], "messages"))
      g_use_messages = true;
    else if(!strcmp(argv[1], "bytes"))
      g_use_messages = false;
    else
    {
      puts(USAGE);
      return 1;
    }
  
    if(g_use_messages && argc == 5)
      g_output_topic = string(argv[4]);
    else if(!g_use_messages && argc == 6)
      g_output_topic = string(argv[5]);
    else
      g_output_topic = g_input_topic + "_throttle";
  
    if(g_use_messages)
    {
      if(argc < 4)
      {
        puts(USAGE);
        return 1;
      }
      g_period = ros::Duration(1.0/atof(argv[3]));
    }
    else
    {
      if(argc < 5)
      {
        puts(USAGE);
        return 1;
      }
      g_bps = atoi(argv[3]);
      g_window = atof(argv[4]);
    }
  
    ros::NodeHandle n;
    g_node = &n;
    subscribe();
    ros::spin();
    return 0;
  }
  
  